| The surplus sludge increases rapidly with the increase of sewage treatment capacity,so it is imperative to recycle the sludge.In recent years,the carbon source utilization technology of sludge has become a research hotspot,which can not only realize the reduction of sludge,but also convert organic matter of sludge into SCFAs as the carbon source of wastewater nitrogen and phosphorus removal process.In order to improve the biodegradation capacity of sludge and promote the efficiency of anaerobic fermentation,this paper carried out a series of studies on acid production by anaerobic fermentation of residual sludge pretreatment with FNA and Sophorolipids,and obtained the optimal acid production process conditions.In addition,the mechanism of FNA+ Sophorolipids pretreatment promoting the anaerobic fermentation of residual sludge to produce acid was revealed in terms of the migration and transformation process of organic matter,the damage degree of sludge cells,related enzyme activity and microbial community,so as to provide theoretical support for the actual production.The following conclusions are drawn:(1)Under anaerobic fermentation condition at 30 ℃,different dosages(0,0.025,0.05,0.1,0.2 g/g TS)of Sophorolipids on anaerobic fermentation efficiency of residual sludge: Sophorolipids pretreatment can effectively promote the dissolution of organic matter in sludge,and the concentrations of SCOD,soluble protein,soluble polysaccharide,ammonia nitrogen and phosphate,and DNA contents increase with the increase of Sophoripid dosage.High Sophoripid level can improve the dissolution rate of organic matter in sludge and shorten the pretreatment time.The highest SCFAs values appeared on the 16 th day when the dosage of Sophorolipids was 0.1 and 0.2 g/g TS,which were5.81 and 6.25 times of the blank group,respectively.However,there was no significant difference in acid production between 0.1 g/g TS and 0.2 g/g TS.In addition,considering the cost problem,the optimal addition was determined to be 0.1 g/g TS.It provides a new idea for the technology of enhancing sludge anaerobic acid production by Sophorolipids pretreatment.(2)Under the condition of 30℃ and pH=6.00,the concentrations of FNA were 0,0.297,0.891,1.584 and 2.376 mg/L,respectively.After FNA pretreatment of sludge for3 d,0.1 g/g TS Sophorolipids were added.It was found that the promotion effect of single Sophorolipids pretreatment on sludge anaerobic fermentation acid production was stronger than that of single FNA pretreatment;the optimal acid production conditions were 0.891 mg/L FNA+ 0.1 g/g TS SL,the maximum SCFAs concentration was 2068.6±18.7 mg COD/L on the 13 th day,which was 2.44 times of blank group.When the concentration of FNA continued to rise from 0.891 mg/L,the SCFAs and acetic acid concentration decreased,indicating that excessive FNA concentration was not conducive to sludge anaerobic fermentation acid production and acetic acid production.This is because high concentration of FNA inhibit the Acid production and hydrolysis of microorganism.The maximum SCOD was 5500± 77.9 mg/L,the highest concentrations of soluble protein and polysaccharide reached 2317.5± 75.8 mg COD/L、563.6± 16.8mg COD/L,and the release of nitrogen and phosphorus was also high.(3)Mechanism analysis showed that coupling pretreatment had stronger damage to the membrane and nucleus of sludge cells,which could significantly improve the biodegradation capacity of sludge and promote the dissolution of intracellular organic matter,resulting in the rapid increase of organic matter content in the TB-EPS layer,and some organic matter was transferred from the TB-EPS layer to the LB-EPS layer and finally to the S-EPS layer.According to the change trend of the concentration of each organic matter in S-EPS layer,it was found that under coupled pretreatment conditions,FNA and Sophorolipids could effectively promote the dissolution of protein in sludge within 48 h and 3d,respectively,and effectively promote the dissolution of polysaccharide in sludge within 36 h and 7d.In addition,the coupled pretreatment had positive effect to the sludge hydrolysis and acidification by promoting the protease,glycosidase enzymes and acetate kinase activity and inhibited methanogens,which increased SCFAs accumulation.In the coupled treatment group,the abundance of Firmicutes involved in anaerobic hydrolysis and acidification was 68.13%,while the abundance of Chloroflexi,Proteobacteria decreased,which are related to organic acid consumption.The dominant genus was Bacillus(37.20%),whose abundance was much higher than that of other bacteria.The coupled pretreatment of 0.891 mg/L FNA+ 0.1 g/g TS SL was beneficial to the enrichment of the dominant bacteria of hydrolysis and acidification,and the abundance ratio of SCFAs consuming bacteria was reduced,thus improving the acid production efficiency of sludge fermentation. |
PDF Full Text Request